This invention relates to a reflector lamp having a reflecting section with faceted surfaces. More particularly, this invention relates to such a reflector lamp which provides improved luminous efficiency by virtue of such faceted surfaces.
Known types of reflector lamps, such as floodlights, automotive headlamps and spotlights, comprise a concave reflector and a light source. The light source is recessed in the concave reflector which reflects frontwardly more than half of the total light output of the lamp. Well-designed reflector lamps for display applications such as PAR 20, PAR 30 and PAR 38 lamp types, provide a visually uniform spot of light of a specified angular width. The luminous efficiency of this cone of light (beam) is an important parameter. Lamp makers are making great efforts in order to achieve even a slight further increase in luminous efficiency. The quantity of light in the beam can be increased by deeply recessing the light source in the reflector while at the same time making the light source as small as possible, or for a fixed source size keeping the reflecting surface as far away from the source as possible.
As disclosed in U.S. Pat. No. 4,447,865 issued to Van Horn, Putz and Henderson, Jr. on May 8, 1984, an improved luminous efficiency and a beam pattern substantially circumferentially uniform about the lamp axis and a reasonably compact reflector lamp can be achieved by a concave reflector having a faceted parabolic front section, a spherical intermediate section and a parabolic rear section. Each section has substantially the same common focal point, and a filament light source is located transversally to the lamp axis at the substantially common focal point. The reflector sections are dimensioned so that substantially all light rays coming from the filament light source which are reflected by the spherical intermediate section become reflected by the faceted parabolic front section. The spherical intermediate section allows more of the light rays that are emanated by a long light source which otherwise would not initially strike the parabolic front section to be directed so as to become re-reflected by the parabolic front section. Additionally the light rays, reflected by the facets, include components thereof which are circumferential about the lamp axis and thereby provide a beam pattern which is substantially circumferentially uniform about the lamp axis.
Tungsten halogen filament tubes, mounted axially in the reflector, have generally replaced incandescent filaments as they provide a larger luminous efficiency and also provide whiter light. Filaments are long and have small diameters. When the halogen filament light tubes are axially positioned in the reflector, the facets make the diameter images appear to be larger and to approach the filament length image.
U.S. Pat. No. 4,494,176 of Sands, Marella and Fink, Jr. issued on Jan. 15, 1985 discloses a reflector lamp which may be of the parabolic aluminized reflector (PAR) type lamp. This prior art reflector lamp has a reduced amount of internal absorption and the internal reflective surfaces direct the light rays into the useful beam pattern more advantageously. Instead of the facets on the parabolic front section, the enhanced light output is achieved by subdividing the intermediate section disclosed in U.S. Pat. No. 4,447,865 into further intermediate sections.
This prior art type reflector lamp comprises a concave reflector and a finite light source positioned axially in the reflector. The geometric center of the light source is located approximately at the focal point of the concave reflector. The concave reflector comprises a parabolic reflective section and at least first and second additional parabolic sections. The first and the second additional parabolic sections are reflective and have a substantially common focal point confocal with the focal point of the concave reflector.
The prior art type reflector lamp comprises a further technical improvement. The subdivided intermediate sections, namely the first and second parabolic sections are aligned relative to the light source positioned approximately at the focal point of the concave reflector, i.e., at the focal point of the main parabolic reflective section. This alignment results in a further improved beam pattern. The first and the second additional sections are so aligned relative to the light source as to be effective to reflect light rays impinging on their surfaces onto the primary parabolic reflective section and thereby direct the light rays in an improved beam pattern. Nevertheless, in the case of elongated and axially positioned light sources, particularly halogen gas filament tubes, most of the light and infrared rays reflected by the intermediate section of the reflector go back to the light source itself which partly absorbs, partly scatters these rays. This phenomenon decreases the light output of the reflector lamp on one hand, and increases the temperature of the light source envelope on the other. The increased heat adversely influences the seal integrity and lumen maintenance of the halogen gas filament tube and brings about a premature darkening of the tube envelope.
Accordingly, an object of the present invention is to provide a reflector lamp, particularly a parabolic aluminized sealed halogen reflector lamp, with increased luminous efficiency. This object can be achieved by reducing or substantially eliminating the light absorbed or scattered by the light source.
In order to achieve these objects and advantages, our invention provides a reflector lamp comprising a substantially parabolic primary reflecting section, a substantially parabolic or substantially spheric secondary reflecting section joined to the primary reflecting section, and a tertiary (or bottom-side ring) reflecting section joined to the secondary reflecting section. The primary, secondary and tertiary sections form substantially a concave reflector with a a substantially planar, parabolic or spheric rear section joined to the tertiary reflecting section 15. The reflector is provided with an incandescent halogen or discharge light source.
The secondary reflecting section has faceted surfaces longitudinally extending along the surface thereof so that a substantial portion of the light reflected thereby avoids the light source and the light absorbed or scattered by the light source is reduced. The tertiary or bottom-side ring refleting section also has faceted surfaces longitudinally extending along the surface thereof, preferably the same number as in the secondary reflecting section. Preferably, the faceted surfaces in the tertiary reflecting section are in phase with the faceted surfaces in the secondary reflecting section; meaning that the faceted surfaces of both the secondary and tertiary reflecting sections are substantially aligned with one another.
In a preferred embodiment of the reflector lamp, the focal point of the secondary reflecting section is axially aligned relative to the focal point of the primary parabolic reflecting section toward the apex of the parabolic reflecting section so that the secondary reflecting section gives room for the ferrule seals needed to provide hermeticity. Preferably, the focal point of the tertiary reflecting section is confocal with the focal points of the primary and secondary reflecting sections so that the tertiary reflecting section gives room for the ferrule seals needed to provide hermeticity.
In an alternate embodiment of the reflector lamp, the faceted surfaces of the secondary and tertiary reflecting sections are circumferentially alternately declined from and inclined to the tangent of the surface at an angle so that substantially all of the reflected light avoids the light source.